1. Field of the Invention
The present invention generally relates to a planar lightguide circuit (PLC) for use in wavelength-division multiplexing/demultiplexing optical communication systems and, in particular, to a packaging device for aligning a planar lightguide circuit and an optical-fiber block to produce a combined single module.
2. Description of the Related Art
In general, a wavelength-division-multiplexing (WDM) communication system involves transfers of multiple wavelengths of optical signals on a single strand of fiber. At the receiving ends, the optical signal received is divided into a plurality of optical signals with a respective wavelength and then converted into electrical signals. To this end, an arrayed-waveguide-grating (AWG) is mainly utilized in the receiving ends to effect such division of the optical signal into multiple wavelengths.
Recently, much research has been focused in the field of optical communication, in particular, on the integration of planar-lightguide-circuit (PLC) elements for forming an optical-waveguide element on a planar substrate. As such, the PLC is used for processing optical signals in a variety of operations, such as branching, modulation, switching, or multiplexing/demultiplexing of the optical signals. The PLC incorporates optical waveguides, which are used for propagating optical signals along the length, i.e., in the longitudinal direction, of an optical-fiber cable. The optical waveguides, consisting of a core member with a high refractive index and a cladding member with a low refractive index, are typically formed by multiple thin layers of silica or polymer on the silicon or quartz substrate and serve various functions such as splitting an optical signal, changing its path or adjusting its light intensity based on the difference in the refractive index between the core and its surrounding cladding.
Referring to FIGS. 1 and 2, a prior-art packaging device for fabricating a planar-light-guide-circuit (PLC) 10 will be explained hereinafter. For simplicity and clarity, a discussion pertaining to well-known components of the PLC and an adhesion means (B) in FIG. 2 is omitted. As shown in FIGS. 1 and 2, the PLC element 10 includes a set of aligned optical-fiber blocks 20 and 30 for receiving and outputting an optical signal. The input optical-fiber block 20 and the output optical-fiber block 30 are positioned in alignment with an input port 12a and output ports 18a of the PLC 10, respectively, for supporting the optical-fiber cables (a single fiber-optic cable F1 or a ribbon-type, fiber-optic cable F2). The optical cables are generally disposed in a V-shaped groove (not shown) formed on a silicon substrate and fixed to the input port 12a and the output ports 18a of the PLC 10 by an adhesion material (B), i.e., epoxy resins. The PLC 10 operates to multiplex wavelengths, in which a multiple wavelength signal is inputted into an input waveguide 12 and the respective multiplexed wavelength appears at each output waveguide 18. The PLC 10 further includes an input waveguide 12 provided before an arrayed waveguide grating (AWG) and an output waveguides 18 provided after the arrayed waveguide grating in opposite end. A first start coupler 14 and a second star coupler 16 are disposed between the input waveguide and the output waveguides before and after the arrayed waveguide grating.
The prior-art packaging device as described above is configured so that the input optical-fiber block 20 is in alignment with and fixed to the input port 12a of the input waveguide using a precise position-control device (not shown). Similarly, the output optical-fiber block 30 is in alignment with and fixed to the output ports 18a of the output waveguides using the same positioning device. Both blocks are then sealed into a housing (not shown) to complete the packaging. As such, multiple optical signals received by the single fiber-optic cable F1 and pass through, sequentially, the input port 12a, input waveguide 12, first star coupler 14, arrayed-waveguide-grating (AWG), second star coupler 16, output waveguides 18, and output ports 18a, toward the ribbon-type fiber-optic cable F2. Furthermore, glass upper plates G1 to G4 are provided to enhance the stability of those components, such as the PLC 10, the input or output optical-fiber blocks 20 and 30, during the manufacturing process. However, the prior-art planar-light-guide circuit has drawbacks in that it is necessary to align each of the input/output optical-fiber blocks 20 and 30 with the corresponding input and output ports 12a and 18a, then project a wide-band laser signal thereto and then make a measurement on each wave-guide using a proper optical-power-measuring device, i.e., an optical lens (not shown), to make sure the alignment and packaging are properly completed.
FIGS. 3 and 4 describe another prior-art-packaging device, which includes a beam splitter 110 and a pair of input and output optical-fiber blocks 120 and 130, each coupled in alignment with the input end and the output end of the beam splitter 110. The beam splitter 110 is provided with an input waveguide 112 and a plurality of output waveguides 114 branched out from the input waveguide 112, forming a Y-shaped branched connection of waveguides. A single fiber-optic cable 122 is connected to the input optical-fiber block 120, and a ribbon-type fiber-optic cable 132 is connected to the output optical-fiber block 130. The beam splitter 110 is also provided with an input port 112a and output ports 114a respectively at both opposite ends, such that the input port 112a is disposed at one end of the beam splitter 110 facing the input optical-fiber block 120, while the output ports 114a are disposed at both opposite ends facing the output optical-fiber block 130. Due to the complexity in the structure, it is often difficult to precisely align the input and output optical-fiber blocks with respect to the input and output ports of the optical waveguide including the beam splitter. In particular, it requires twice as much time to implement the alignment processes, i.e., first aligning the input optical-fiber block with the planar lightguide circuit and then aligning the output optical-fiber block in a similar manner. As a result, productivity and reliability are compromised. In addition, the thermal deformation that may occur in the course of bonding the optical elements with any adhesive material or epoxy resin during the alignment process will also produce an adverse effect on reliability. Furthermore, the prior-art alignment scheme of the planar lightguide circuit usually requires at least two optical-fiber blocks, spaced apart opposite to each other, such that the total size or volume of the associated optical module is undesirably large.